1. Cooling System Architecture Design for FCS Hybrid Electric Vehicle
Sungjin Park, Dohoy Jung, Zoran Filipi, and Dennis Assanis
The University of Michigan
In collaboration with Thrust Area 5

2. Outline Background Motivation and Challenges Objectives
SHEV Configuration
Cooling System Component Modeling
Cooling System Architecture
Results and Discussion
Summary and Future Plan

3. Army Ground Vehicle Propulsion Challenges
Cooling
Fuel Effects
Filtration
The Army vehicle cooling point is high tractive effort to weight under desert-like operating conditions (ex. 5 ton wheeled vehicle ~0.6 while 15 ton tracked vehicle ~0.7 both at 120 F ambient)
This slide is from the keynote by Dr. Pete Schihl during the 2007 ARC annual conference

4. Future Combat System (FCS)
Series Hybrid Electric Vehicle (SHEV) is under development for the automotive platform of FCS.
Improved fuel economy
Greater electric power requirements for advanced weapon system
Exportable electric power
Enhanced low speed maneuverability
Low acoustic signature and stealth operation
Pulse power necessary to drive weapon/mobility/communication/protective systems
Better maintenance: non-mechanical coupling of the power generation unit with drive train architecture

5. Case Study Objectives
Develop a guideline/methodology for cooling system architecture selection for the SHEV
Develop cooling system models for optional architectures.
Explore and demonstrate proper architectures and strategies for thermal management of hybridized powertrain
Optimize the cooling system and component design for performance, size and minimal parasitic loss

6. Motivation and Challenges
SHEVs need additional components
Generator, Motor, Battery, and Power bus
SHEVs also have a dedicated cooling system for the hybrid components with different requirements
Cooling system design for SHEV requires more strategic approach
Multiple cooling circuits due to additional components
Different operating temperature and driving modes
Numerical approach is an efficient way for complicated HEV cooling system design and development.

7. Vehicle Cooling system for Future Combat System (FCS): Challenges
Component
Heat load (kW)
Control Target Temp.
(oC)
Engine
190
120
Oil cooler 40
125
Charge air cooler 13 -
Motor 27 95
Generator 65
Power bus
5.9 70
Battery 12 45
SHEV Cooling System
Heavy-duty operation (20 ton, hp vehicle)
Severe military operation under extreme ambient conditions
Shielded cooling system for survivability
Complicated cooling system architecture in SHEV due to the additional heat sources with various requirements
Vehicle cooling system operation and performance varies with powertrain operation, control, and driving conditions.
Conventional Cooling System

8. Objectives
Develop an efficient cooling system architecture for the SHEV and Optimize the cooling system design using numerical approach:
Configure a SHEV model using VESIM
Model the components of the cooling system for SHEVs
Develop cooling system model integrating the components models
Evaluate the cooling system designs and architectures
Optimize the cooling system
SHEVs need effective cooling system design that has least impact on fuel economy and cost

9. SHEV Configuration (VESIM)
Engine
400 HP
(298 kW)
Motor
2 x 200 HP (149 kW)
Generator
Battery
(lead-acid)
18Ah /
120 modules
Vehicle
20,000 kg (44,090 lbs)
Maximum speed
45 mph
(72 kmph)
Engine
Generator
Vehicle
Motor
Battery
Controller
Power
Bus

10. Power Management of Hybrid Vehicle
Charging/Electric Drive mode
Discharging mode
Braking mode
Battery is the prime power source
When power demand exceeds battery ability, the engine is activated to supplement power demand
Engine/Generator is the prime power source
When battery SOC is lower than limit, engine supplies additional power to charge the battery
Once the power demand is determined, engine is operated at most efficient point
Regenerative braking is activated to absorb braking power
When the braking power is larger than motor or battery limits, friction braking is used

11. Vehicle Cooling System Simulation (VCSS)
SIMULINK Based Vehicle Cooling System Simulation
Component
Approach
Implementation
Heat Exchanger
Thermal resistance concept 2-D FDM
Fortran (S-Function)
Pump
Performance data-based model
Matlab/Simulink
Cooling fan
Thermostat
Modeled by three-way valve
Engine
Map-based performance model
Engine block
Lumped thermal mass model
Generator
Power bus
Motor
Oil cooler
Heat exchanger model (NTU method)
Turbocharger
Condenser
Heat addition model
Charge air cooler

12. Vehicle Cooling System Simulation (VCSS)
SIMULINK Based Vehicle Cooling System Simulation
Heat Source Components
Component
Heat generation model
Heat transfer model
Pressure drop model
Engine
Map-based performance model
Lumped thermal mass model
Experimental correlation:
Generator
Flow in smooth pipe
Laminar:
Turbulent:
Power bus
Battery is charged and motor is working
Motor is working
Motor is generating
Motor
Motor:
Generator:
Turbocharger
N/A

13. Vehicle Cooling System Simulation (VCSS)
SIMULINK Based Vehicle Cooling System Simulation
Heat Sink Components
Component
Heat generation model
Heat transfer model
Pressure drop model
Radiator
N/A
Thermal resistance concept 2-D FDM [8]
Water side :
Air side :
Condenser
Heat from A/C module is assumed to be constant
Heat addition model
Charge air cooler
Thermal resistance concept 2-D FDM
Oil cooler
Heat Source
Map-based performance model
Heat
Exchanger
Heat exchanger model (NTU method) [9]
Flow in smooth pipe
Laminar:
Turbulent:
Oil Pump
Performance data-based model

14. Vehicle Cooling System Simulation (VCSS)
SIMULINK Based Vehicle Cooling System Simulation
Delivery Media Components
Component
Flow rate model
Heat transfer model
Pressure drop model
Pump
Performance data-based model
N/A
Cooling fan
Thermostat
Modeled by a pair of valves
Lumped thermal mass model

15. Cooling System Architecture Development
Architecture A
Separate cooling circuit is added for electric components.
Electric pumps are used for electric heat sources to separate the cooling circuit for electric components from engine module
The radiators are arranged in the order of control target temperature of heat source which is cooled by the radiator

16. Cooling System Architecture Development
Architecture A
Architecture B
Component
Control target temp. (oC)
Engine
120
Motor / controller 95
Generator / controller
Charge air cooler -
Oil cooler
125
Power bus 70
Battery 45
Control Target Temp.
of Heat Sources
Cooling circuit for electric components is further divided into two circuits based on control target temperatures.
Electric pumps are used for electric heat sources to separate the cooling circuit for electric components from engine module
The radiators are arranged in the order of control target temperature of heat source which is cooled by the radiator.

17. Cooling System Architecture Development
Architecture C
Component
Operation group
Engine A
Motor / controller B
Generator / controller
Charge air cooler
Oil cooler
Power bus C
Battery -
Operation Group of Heat Sources
Cooling Module 1
Cooling Module 2
(1)The heat source components are allocated into two cooling modules based on the operating groups to minimize redundant operation of the cooling fan.
(2) The condenser used for the air conditioning of the compartment is placed in the cooling module where the heat load is relatively lower.

18. SIMULINK Based Vehicle Cooling System Simulation Vehicle Cooling System Simulation (VCSS)
Cooling circuit for electric components
A/C
Condenser
Electric Components
Parallel
Cooling
Circuit
Coolant
pump
Radiator1
Cooling circuit for engine module
Charge Air
Cooler
Parallel
Cooling
Circuit
Oil
Cooler
Engine
Engine
Block
Thermostat
Coolant
pump
Radiator2
Fan &
cooling air

19. Sequential SHEV-Cooling System Simulation
Operation history of each HEV component from VESIM is fed into Cooling system Model as input.
Better computational efficiency compared to co-simulation
Driving schedule
Hybrid Vehicle Model
Cooling System Model

20. Cooling System Test Conditions
Three driving were selected to size the components of cooling system and to evaluate cooling system design performance
Grade Load
Maximum Speed
(Governed)
Off-Road
Ambient Temperature : 40 oC
Road profile for off-road

21. Power Consumption of Cooling System (Grade load condition)

22. Driving Schedule for the Evaluation of Cooling System
Realistic driving schedule is needed to evaluate the cooling system
City + Cross country driving schedule is used
Component
Operation group
Engine A
Motor / controller B
Generator / controller
Charge air cooler
Oil cooler
Power bus C
Battery -
Operation Group of Heat Sources
City + Cross country
Driving Schedule
Heat Rejection Rate of
Each Component over Driving Schedule

23. Power Consumption and Cooling Performance during Driving Schedule
Electric Component Temperature

24. Cooling System Power Consumptions
Improvement of Power Consumption
by Cooling System Redesign
Portion of Cooling System
Power Consumption in Engine Power

25. Summary and Future Plan
SHEV model was configured with the previously developed VESIM.
Cooling system model for the SHEV was developed.
The results show that strategic approach to cooling system architectural design of SHEVs can reduce the power consumption and enhance the performance significantly.
Co-simulation of VESIM and Cooling system model is needed to evaluate
Fuel economy impact
Interaction between the powertrain system and cooling system